The Mackinaw River in central Illinois contains some of the highest quality tributaries remaining in the state; however, stream biodiversity is threatened by agricultural practices that dominate land use within the watershed. Rapid transport of subterranean tile-drained waters from agricultural fields contributes to streambank erosion, high nutrient loading, and loss of wetland habitat throughout the watershed. We have estimated that 37-351 metric tons of NO₃-N were transported annually into the Mackinaw River mainstem from just 2 of 32 subwatersheds in the basin during the past 6 years. Our current research is designed to measure how much farmland could be converted to wetlands to effectively reduce agricultural nutrient inputs to the river. We have worked with landowners to develop a 250-acre demonstration farm with 3 tile-drained wetland units, each consisting of a series of three wetlands that drain 3-9% of the surrounding farmland. Control gates and monitoring equipment set at inlets and outlets of the 9 wetlands are used to monitor water quality. Preliminary results calculated from variable rates of flow and time periods show 51-99% retention of NO₃-N by wetlands representing 3% of the drainage area during late spring and early summer.